Which of the following statements about work is or are true? (More than one statement may be true.) A) Negative net work done on an object always reduces the object’s kinetic energy.
The correct answer and explanation is:
Let’s analyze statement A:
A) Negative net work done on an object always reduces the object’s kinetic energy.
Is this statement true?
Yes, this statement is true based on the work-energy theorem.
Explanation:
Work and Kinetic Energy Relationship
The work-energy theorem states that the net work done on an object equals the change in its kinetic energy: Wnet=ΔKE=KEfinal−KEinitialW_{net} = \Delta KE = KE_{final} – KE_{initial}
- If net work WnetW_{net} is positive, the object’s kinetic energy increases.
- If net work WnetW_{net} is negative, the object’s kinetic energy decreases.
What does negative net work mean?
Negative net work means that the forces acting on the object are doing work opposite to the direction of the object’s motion, effectively removing energy from the object. This reduces the speed of the object and therefore reduces its kinetic energy.
For example:
- When friction acts on a moving box sliding on the floor, it does negative work because friction force opposes the motion. The box slows down, losing kinetic energy.
- When you apply the brakes on a moving car, the brakes do negative work, reducing the car’s kinetic energy and slowing it down.
Can negative work ever increase kinetic energy?
No, by definition, negative net work cannot increase kinetic energy. It always leads to a decrease in kinetic energy.
Summary
- Negative net work means energy is taken away from the object.
- This always causes a decrease in kinetic energy.
- Thus, statement A is true.